1. Technical Field
The present disclosure relates generally to a surgical apparatus for fusing adjacent bone structures, and, more particularly, to an apparatus and method for fusing adjacent vertebrae.
2. Background of the Related Art
The fusion of adjacent bone structures is commonly performed to provide for long-term replacement to compensate for degenerative or deteriorated disorders in bone. For example, an intervertebral disc, which is a ligamentous cushion disposed between adjacent vertebrae, may undergo deterioration as a result of injury, disease, tumor or other disorders. The disk shrinks or flattens leading to mechanical instability and painful disc translocations.
Conventional procedures for disc surgery include partial or total excision of the injured disc portion, e.g., discectomy, and replacement of the excised disc with biologically acceptable plugs or bone wedges. The plugs are driven between adjacent vertebrae to maintain normal intervertebral spacing and to achieve, over a period of time, bony fusion with the plug and opposed vertebrae. For example, U.S. Pat. No. 4,887,020 to Vich discloses a cylindrical bone plug having a thread on its exterior, which is screwed into a correspondingly dimensioned cylindrical bore drilled in the intervertebral space. Other bone grafting plugs are disclosed in U.S. Pat. No. 4,950,296.
More recently, emphasis has been placed on fusing bone structures (i.e., adjoining vertebrae) with prosthetic cage implants. One fusion cage implant is disclosed in U.S. Pat. No. 5,026,373 to Ray et al. The Ray '373 fusion cage includes a cylindrical cage body having a thread formed as part of its external surface and apertures extending through its wall which communicate with an internal cavity of the cage body. The fusion cage is inserted within a tapped bore or channel formed in the intervertebral space thereby stabilizing the vertebrae and maintaining a pre-defined intervertebral space. The adjacent vertebral bone structures communicate through the apertures with bone growth inducing substances within the internal cavity to unite and eventually form a solid fusion of the adjacent vertebrae. Other prosthetic implants are disclosed in U.S. Pat. Nos.: 4,501,269; 4,961,740; 5,015,247; and 5,489,307.
Fusion implants or cages of the type aforedescribed are typically made from a biocompatible rigid material such as titanium or titanium alloys, ceramics, stainless steel, etc. These implants become permanently fixed within the spinal column as a result of the fusion process to remain in the patient indefinitely.
Recent emphasis has been placed on the use of synthetic bioabsorbable polymers for the manufacture of implantable surgical devices such as surgical fasteners, clips, staples and sutures. An advantage of the bioabsorbable devices is that they degrade and are absorbed by the body over a period of time. Ideally, the bioabsorbable surgical device maintains its strength for as long as it takes the body tissue to heal and, thereafter, rapidly degrades and disappears.